The subject invention concerns an element designed to align coupling members on end fittings during concrete pile casting. The end fittings used for this purpose have key grooves formed therein, each such groove being designed, when two concrete pile sections are to be joined together in end-to-end position, to receive a locking key therein to interconnect the end fitting at one of the ends of one concrete pile section with a matching end fitting arrangement at the opposed end of the other pile section. At the bottom of each key groove is arranged a through-passage with a recessed seat therein to accommodate the coupling member which rests freely in the seat and which is coupled to a reinforcement iron rod extending lengthwise through the concrete pile.
As a rule, concrete piles are manufactured in sections of suitable lengths and have a core made up of lengthwise reinforcement iron rods about which wires are wound to form a reinforcement cage. A coupling member is screwed onto each end of the reinforcement rods and extends through an end fitting provided at each end of the core.
It is already known to arrange the head of the coupling member freely supported in a seat in the end fitting. When interconnected concrete pile sections are driven in end-to-end position into the ground tensile stress that occurs between the blows will be efficiently taken by the reinforcement irons while at the same time the movability of the coupling member relative to the end fitting serves to avoid that the thrust during the driving-down operation damages the reinforcement rods, which may result in the entire pile section having to be rejected. Such damage and ensuing rejection is not uncommon when the coupling members are rigidly connected with the end fitting or when the reinforcement rods are welded directly onto the end fitting.
However, in some already cast concrete piles it has been found that one or several of the coupling members do not always assume a correct position in their respective seats, aligned with and in abutment against the associated end fittings. As a result, it may not be possible to insert the locking keys into the associated key grooves to join together two pile sections. Furthermore, even when the locking keys can be inserted into their associated grooves the axial play is often too small between the free end of the coupling member and the locking key positioned externally thereof. The result is that the intended effect is lost, that is, the ability of the coupling member to move axially when exposed to the effects of impacts from the driving-down apparatus.
One reason for the occurrence of the problem outlined above is the time lag between the arrangement of the reinforcement cage in alignment with the end fittings in the casting mold and the casting operation proper. It has been found that the axial play between the coupling member and the blocking key should be at least 3 millimeters. In concrete casting vibrator means are used to ensure that the concrete fills out the casting mold entirely. Also the vibrations may contribute to the occurrence of insufficient axial play.